DSPIC30F4013-20I Datasheet, PDF (128/220 Pages) Microchip Technology – High-Performance, 16-Bit Digital Signal Controllers

dsPIC30F3014/4013
19.1 A/D Result Buffer
The module contains a 16-word dual port read-only
buffer, called ADCBUF0...ADCBUFF, to buffer the A/D
results. The RAM is 12 bits wide but the data obtained
is represented in one of four different 16-bit data for-
mats. The contents of the sixteen A/D Conversion
Result Buffer registers, ADCBUF0 through ADCBUFF,
cannot be written by user software.
19.2 Conversion Operation
After the A/D module has been configured, the sample
acquisition is started by setting the SAMP bit. Various
sources, such as a programmable bit, timer time-outs
and external events, terminate acquisition and start a
conversion. When the A/D conversion is complete, the
result is loaded into ADCBUF0...ADCBUFF, and the
DONE bit and the A/D interrupt flag, ADIF, are set after
the number of samples specified by the SMPI bit. The
ADC module can be configured for different interrupt
rates as described in Section 19.3 “Selecting the
Conversion Sequence”.
The following steps should be followed for doing an
A/D conversion:
1. Configure the A/D module:
• Configure analog pins, voltage reference and
digital I/O
• Select A/D input channels
• Select A/D conversion clock
• Select A/D conversion trigger
• Turn on A/D module
2. Configure A/D interrupt (if required):
• Clear ADIF bit
• Select A/D interrupt priority
• Set ADIE bit (for ISR processing)
3. Start sampling
4. Wait the required acquisition time
5. Trigger acquisition end, start conversion:
6. Wait for A/D conversion to complete, by either:
• Waiting for the A/D interrupt, or
• Waiting for the DONE bit to get set.
7. Read A/D result buffer, clear ADIF if required
19.3 Selecting the Conversion Sequence
Several groups of control bits select the sequence in
which the A/D connects inputs to the sample/hold
channel, converts a channel, writes the buffer memory
and generates interrupts.
The sequence is controlled by the sampling clocks.
The SMPI bits select the number of acquisition/
conversion sequences that would be performed before
an interrupt occurs. This can vary from 1 sample per
interrupt to 16 samples per interrupt.
The BUFM bit splits the 16-word results buffer into two
8-word groups. Writing to the 8-word buffers is alter-
nated on each interrupt event.
Use of the BUFM bit depends on how much time is
available for moving the buffers after the interrupt.
If the processor can quickly unload a full buffer within
the time it takes to acquire and convert one channel,
the BUFM bit can be ‘0’ and up to 16 conversions (cor-
responding to the 16 input channels) may be done per
interrupt. The processor has one acquisition and
conversion time to move the sixteen conversions.
If the processor cannot unload the buffer within the
acquisition and conversion time, the BUFM bit should be
‘1’. For example, if SMPI<3:0> (ADCON2<5:2>) = 0111,
then eight conversions are loaded into 1/2 of the buffer,
following which an interrupt occurs. The next eight con-
versions are loaded into the other 1/2 of the buffer. The
processor has the entire time between interrupts to
move the eight conversions.
The ALTS bit can be used to alternate the inputs
selected during the sampling sequence. The input
multiplexer has two sets of sample inputs: MUX A and
MUX B. If the ALTS bit is ‘0’, only the MUX A inputs are
selected for sampling. If the ALTS bit is ‘1’ and
SMPI<3:0> = 0000 on the first sample/convert
sequence, the MUX A inputs are selected and on the
next acquire/convert sequence, the MUX B inputs are
selected.
The CSCNA bit (ADCON2<10>) allows the S/H input to
be sequentially scanned across a selected number of
analog inputs for the MUX A group. The inputs are
selected by the ADCSSL register. If a particular bit in
the ADCSSL register is ‘1’, the corresponding input is
selected. The inputs are always scanned from lower to
higher numbered inputs, starting after each interrupt. If
the number of inputs selected is greater than the
number of samples taken per interrupt, the higher
numbered inputs are unused.
Note:
The ADCHS, ADPCFG and ADCSSL reg-
isters allow the application to configure
AN13-AN15 as analog input pins. Since
these pins are not physically present on
the device, conversion results from these
pins read ‘0’.
DS70138E-page 126
© 2007 Microchip Technology Inc.